Consumable electrode vacuum furnace

ABSTRACT

A lock chamber fixedly superimposed on the open top of the crucible in a consumable-electrode vacuum furnace, and an opening through the chamber permits the tank holding the electrode to be set directly on the crucible rim during normal furnace operation. A flange mounted on the tank by means of a pliable annular diaphragm seals the tank to the lock chamber while the tank moves. A valve plate in the chamber can be moved over the crucible top to seal the crucible while the tank with the electrode in the same is lifted, the tank is thereafter lowered upon the valve plate to hold in sealing engagement with the crucible top, and air can enter the lock chamber thereafter through the tank without impairing the vacuum in the crucible.

United States Patent Samietz et al.

1451 May 23, 1972 [54] CONSUMABLE ELECTRODE VACUUM FURNACE [72] Inventors: Klaus P. Samietz, Monroeville, Pa; Anton Wamser, Hanau Main; Ernst F. Weingartner, Hailer, both of Germany Primary Examiner-Bemard A. Gilheany Assistant Examiner-Roy N. Envall, Jr. Attorney-Joseph F. Padlon ABSTRACT A lock chamber fixedly superimposed on the open top of the crucible in a consumable-electrode vacuum furnace, and an opening through the chamber permits the tank holding the electrode to be set directly on the crucible rim during normal furnace operation. A flange mounted on the tank by means of a pliable annular diaphragm seals the tank to the lock chamber while the tank moves. A valve plate in the chamber can be moved over the crucible top to seal the crucible while the tank with the electrode in the same is lifted, the tank is thereafter lowered upon the valve plate to hold in sealing engagement with the crucible top, and air can enter the lock chamber thereafter through the tank without impairing the vacuum in the crucible.

5 Claims, 5 Drawing Figures Patented May 23, 1972 5 Sheets-Sheet 2 FIG. 3

Patented May 23, 1972 3 Sheets-Sheet 3 Inventor 1 WW I3'U,W}P

CONSUMABLE ELECTRODE VACUUM FURNACE This invention relates to consumable-electrode vacuum furnaces, and particularly to the vacuum-tight sealing of the furnace portion containing the molten metal during the solidification of the latter.

It is known to equip a furnace of the general type described with a lock chamber attached to the melt-containing lower portion of the furnace shell, valve plate and mechanism for moving the valve plate toward and away from an operating position in which the valve plate closes the open upper end of the shell portion are arranged in the lock chamber. The electric arc passing between the molten metal in the lower shell portion and an electrode in an upper, movable portion of the furnace shell generates a mist or spray of metal droplets which tend to enter the lock chamber and to interfere with reliable operation of the valve moving mechanism even if provisions are made for preventing them from fouling the sealing surface of the valve plate. However, the known devices are only partly successful in preventing deposition of spattered metal on the sealing face of the lower shell portion intended for engagement with the valve plate. The known devices rely only on the relatively small weight of the valve plate and on the pressure differential between the ambient atmosphere and the vacuum in the lower shell portion for holding the valve plate in sealing engagement with the lower shell portion. The metal particles spattered on the sealing face of the shell portion opposite the valve plate retard sealing engagement between the valve plate and the lower shell portion, and the air initially admitted to the lower shell portion is detrimental to the quality of the solidifying metal. I

The primary object of the invention is an improved look arrangement in a consumable-electrode vacuum furnace which permits a high vacuum to be maintained in the lower portion of the furnace shell containing the molten metal while the upper portion of the shell on which the electrode is mounted is being removed.

It has been found that the desired vacuum can readily be maintained in the lower furnace shell portion throughout the several stages of furnace operation if the lock chamber is provided with a vertical opening therethrough dimensioned for passage of the upper shell portion toward and away from a position adjacent the lower shell portion in which the upper shell portion abuttingly engages the lower portion, this position being available while the valve member is remote from its operative position. A sealing arrangement seals the shell portions and the lock chamber from the ambient atmosphere during passage of the upper shell portion through the openings in the lock chamber.

The sealing arrangement may include a pliable sealing member having one portion fixedly fastened to the upper shell portion, and another portion which carries an annular flange, relative vertical movement of the two portions being limited by a restraining device. Respective sealing faces on the flange and on the lock chamber are engaged by movement of the upper shell portion into the position adjacent the lower shell portion. When the valve member is in its operative position, it is in the path of the upper shell portion and abuttingly engaged by the latter for tight sealing engagement with the open top of the lower shell portion.

A horizontal sealing face on the lower shell portion about the open upper end of the same is formed with two spacedly juxtaposedannular grooves, and the upper shell portion has two annular ribs which are respectively received in the grooves when the upper shell portion engages the lower portion, whereby an annular portion of the sealing face between the grooves is protected by the upper shell portion. When the valve member is in its operative position, it sealingly engages the annular portion of the sealing face.

Other features, additional objects, and many of the attendant advantages of this invention will readily by appreciated as the same becomes better understood by reference to the following detailed description of a preferred embodiment when considered in connection with the appended drawing in which:

FIG. I shows a consumable electrode furnace of the invention in fragmentary elevational section;

FIGS. 2 to 4 show the device of FIG. I in different operational positions; and

FIG. 5 shows a portion of the device of FIG. 1 on a larger scale in a corresponding view.

Referring to the drawing in detail, and initially to FIG. 1, there is seen only as much of ;an otherwise conventional, consumable-electrode furnace as is necessary for an understanding of the invention. As far as not illustrated, the furnace may be of the type described and illustrated in The Making, Shaping, and Treating of Steel" (edited by Harold E. McGannon, United States Steel, 8th ed., 1964, pages 544-545).

A consumable-electrode 1 is mounted in the upper portion 2 of the generally cylindrical, upright furnace shell by means of a non-illustrated holder arrangement which permits the electrode to be moved coaxially in the shell. The upper shell portion 2 is suspended from a non-illustrated hoist and consists mainly of a double walled tank 3 enveloped by a fixed furnace housing 4 over most of its axial length, the lowermost axial portion of the tank 3 projecting beyond the housing 4 and carrying a pair of flanges 5 fastened to each other. The inner rim of an annular, pliable diaphragm or bellows 6 is clamped in sealing engagement between the two flanges 5, and the outer rim of the diaphragm is attached to a flat, annular flange 7.

In the condition of the furnace illustrated in FIG. 1, springs 9 distributed over the circumference of the housing 4 press the flange 7 into engagement with a flange l0 fixedly mounted atop a lock chamber 11 about the upper orifice of a vertical passage through the chamber. An O-ring 8 (FIG. 2) inserted in the sealing face of the flange l0 tightly seals the lock chamber 11 to the upper shell portion 2 to prevent the admission of ambient atmospheric air, but a short pressure-equalizing conduit 12 connects the interior of the tank 3 with the chamber 11. The portion of the tank 3 not visible in the drawing is normally connected to a vacuum pump, is conventional.

A narrow radial flange 13 about the open lower end of the tank 3 carries an annular sheet metal guard .14, whose function will be presently described with reference to FIG. 5, and abuttingly and sealingly engages a radial flange or rim 15 on a crucible 16 which is the principal element of the upwardly open lower portion of the furnace shell. A pool of molten metal 17 is contained in the crucible l6 and is fed by metal melting from the electrode 1 in the usual manner. The crucible is equipped with a cooling jacket 18 supplied with cold water during furnace operation. A radial, outer flange 19 on the jacket 18 is sealed to the crucible rim or flange l5 and projects radially outwardly beyond the rim 15. The flange 19 is fixedly sealed to an annular flange 20 about the lower orifice of the afore-mentioned vertical passage through the lock chamber 11.

Wheels 21 rolling on rails 22 permit a valve plate 23 to move horizontally in the lock chamber 11 toward and away from the vertical passage through the chamber which, in the position of FIG. 1, is largely occupied by the upper shell portion 2, more specifically the tank 3 and the electrode 1. The remotely control-led mechanism which moves the valve on and beyond the rails 22 has not been shown since it may be entirely conventional. While more sophisticated equipment is normally preferred, the valve moving mechanism may consist of a rod hingedly attached to the valve plate 23, passing outward through a stuffing box in the wall of the chamber 11, not visible in the drawing and equipped with a handle for manual shifting of the valve plate in a manner indicated in the drawing only by an arrow in FIG. 2.

Details of the sealing arrangement which maintains a high vacuum in the crucible 16 even when the tank 3 is removed from the position of FIG. 1, are illustrated in FIG. 5. One of the wheels 21 on the valve plate 23 is shown in phantom view in FIG. 5 to reveal a gasket ring 24 projecting from the underside of the plate 23 and held in position by a frame 31. FIG. 5 also shows similar gaskets 29, 30 interposed between the flange 19 and respectively, the crucible rim 1S and the lower flange 20 on the lock chamber 11 which are fixedly fastened to each other.

The gasket ring 24 is dimensioned for sealing engagement with an annular seating portion 32 on the upwardly directed, horizontal sealing face of the rim 15. The seating portion 32 is bounded by two coaxial, radially spaced, annular grooves 33 in the sealing face of the rim 15. The afore-mentioned annular sheet metal guard 14 has the shape of a downwardly open, shallow channel whose flanges project downwardly from he flange 13 on the tank 3 like two ribs, and are partly received in the grooves 33, whereby the guard 14 envelops the seating portion 32 and protects it against contamination in the position of the furnace shown in FIGS. 1 and 5.

In that position of the furnace, an electric arc passes between the electrode 1, and the metal pool 17, the electrode 1 is gradually consumed, and the molten metal collects in the pool 17. Metal droplets are in turbulent movement in the vacuum above the surface of the pool 17, but cannot enter the lock chamber 11 between the flange 13 on the tank 3 and the rim 15 on the crucible 16 in substantial amounts. The traces of metal which may penetrate the seal between the flange 13 and the rim 15 are prevented by the guard 14 from contaminating the seating portion 32. The conduit 12 is too high above the pool 17 to permit passage of significant amounts of metal droplets. Moreover, it is directed diametrically away from the valve plate 23 and from its non-illustrated moving mechanism.

When the electrode has been consumed to the desired extent, and the crucible 16 holds a sufficient amount of metal, the stump of the electrode is lifted out of the crucible l6, and the tank 3 is lifted sufficiently in the vertical passage of the lock chamber 11 to permit the valve plate 23 to be rolled into its operative position above the open top of the crucible 16, as illustrated in FIG. 2. The vacuum-tight seal between the tank 3 and the lock chamber 11 is maintained during the short upward movement of the tank by the flanges 7, under the pressure of the helical compression springs 9, and by the bellows or diaphragm 6.

When the valve plate 23 reaches its operative position, in which the gasket ring 24 is vertically aligned with the seating portion 32 of the upper face on the rim 15, as shown in FIG. 3, from which the wheels 21 have been omitted for the sake of clarity, the tank 3 is lowered until its weight rests on the top of the valve plate 23, thereby firmly seating the gasket ring 24 on the seating portion 32 of the crucible rim which had been held free from spattered metal by the guard 14 during operation of the electric arc. With the valve plate tightly sealed to the crucible, the non-illustrated vacuum pump is disconnected from the tank 3, and a vent valve, not shown, is opened to admit ambient air to the tank 3 and then to the lock chamber 11. The atmospheric pressure is thereafter sufficient to hold the valve plate 23 in place while the upper furnace portion is lifted from the lower portion for use on another crucible or for replacement of the electrode. Water circulating in the jacket 18 causes solidification of the metal pool 17 in the crucible 16 while a high vacuum is being maintained.

Damage to the pliable diaphragm 6 is prevented by restraining devices 25 respectively associated with the springs 9 when the flange 7 is lifted from the fixed flange 10 on the lock chamber 11. Each restraining device 25 includes a spring receptacle 26 having the shape of an inverted cup from which the spring 9 projects downwardly. The spring is coiled about a rod 27 which passes into the jacket 4 through a non-illustrated packing in the bottom of the receptacle 26. A disc 28 on one end of the rod 27 in the jacket 4 limits downward or outward movement of the rod 27 under the pressure of the spring 9 which is contained between the bottom of the receptacle 26 and another disc at the lower end of the rod 27 fixedly fastened to the flange 7.

The lock arrangement of the invention does not rely for vacuum tightness on sealingly engaged metal surfaces finished to extremely small tolerances, and can therefore be constructed at relatively low cost. It does not require costly maintenance operations for remaining in good working condition because critically important sealing surfaces on the valve plate and on the rim of the crucible are well protected against fouling by metal droplets spattered by the electric arc. The valve drive mechanism, while not specifically illustrated, is similarly protected. The tightness of the seal between the valve plate and the crucible does not depend on the difference in the pressures applied to the opposite faces of the valve plate when air begins to enter the upper portion of the furnace shell in the last stage of the melting cycle, and when the pressure difference is only small.

The furnaces of the invention are therefore more eflective than the afore-described furnaces of prior art, yet their improved lock arrangement is simple and sturdy.

What is claimed is:

1. In a consumable-electrode vacuum furnace having an upwardly open lower shell portion adapted to enclose a body of molten metal; a lock chamber superimposed on said lower shell portion; a valve member movable in said chamber toward and away from an operative position in which said valve member closes the upper end of said shell portion; and a downwardly open upper shell portion mounted for vertical movement toward and away from a position adjacent said lower shell portion in which said shell portions communicate with each other while being sealed from the ambient atmosphere, the improvement which comprises:

a. said lock chamber being formed with an opening vertically therethrough and vertically aligned with said upper end of said lower shell portion;

b. said opening being dimensioned for passage of said upper shell portion therethrough toward and away from said adjacent position thereof while said valve member is remote from said operative portion;

c. said upper shell position in said adjacent portion abuttingly engaging said lower shell portion; and

d. sealing means sealing saidshell portions and said chamber from said ambient atmosphere during said passage of said upper shell portion through said opening.

2. In a furnace as set forth in claim 1, said sealing means including a pliable sealing member having respective portions secured to said upper shell portion and to said lock member and sealingly connecting the same during said passage of said upper shell portion.

3. In a furnace as set forth in claim 2, one of said portions of said sealing member being fixedly fastened to said upper shell portion, the other portion carrying an annular flange, restraining means limiting relative vertical movement of said one portion of said flange, said flange and said lock chamber having respective sealing faces engageable by movement of said upper shell portion into said adjacent position.

4. In a furnace as set forth in claim 1, said valve member when in said operative position being arranged in the path of said upper shell portion toward said adjacent position of the same, whereby said upper shell portion abuttingly engages said valve member in the operative position of the latter, during said passage of the upper shell portion toward said adjacent position.

5. In a furnace as set forth in claim 1, said lower shell portion having a sealing face horizontally extending about said open upper end thereof, and formed with two spacedly juxtaposed annular grooves, said upper shell portion including two annular ribs respectively received in said annular grooves in said adjacent position of said upper shell portion, whereby an annular portion of said sealing face between said grooves is protected by said upper shell portion in said adjacent position of the same, said valve member when in the operative position sealingly engaging said annular portion of said sealing face. 

1. In a consumable-electrode vacuum furnace having an upwardly open lower shell portion adapted to enclose a body of molten metal; a lock chamber superimposed on said lower shell portion; a valve member movable in said chamber toward and away from an operative position in which said valve member closes the upper end of said shell portion; and a downwardly open upper shell portion mounted for vertical movement toward and away from a position adjacent said lower shell portion in which said shell portions communicate with each other while being sealed from the ambient atmosphere, the improvement which comprises: a. said lock chamber being formed with an opening vertically therethrough and vertically aligned with said upper end of said lower shell portion; b. said opening being dimensioned for passage of said upper shell portion therethrough toward and away from said adjacent position thereof while said valve member is remote from said operative portion; c. said upper shell position in said adjacent portion abuttingly engaging said lower shell portion; and d. sealing means sealing said shell portions and said chamber from said ambient atmosphere during said passAge of said upper shell portion through said opening.
 2. In a furnace as set forth in claim 1, said sealing means including a pliable sealing member having respective portions secured to said upper shell portion and to said lock member and sealingly connecting the same during said passage of said upper shell portion.
 3. In a furnace as set forth in claim 2, one of said portions of said sealing member being fixedly fastened to said upper shell portion, the other portion carrying an annular flange, restraining means limiting relative vertical movement of said one portion of said flange, said flange and said lock chamber having respective sealing faces engageable by movement of said upper shell portion into said adjacent position.
 4. In a furnace as set forth in claim 1, said valve member when in said operative position being arranged in the path of said upper shell portion toward said adjacent position of the same, whereby said upper shell portion abuttingly engages said valve member in the operative position of the latter, during said passage of the upper shell portion toward said adjacent position.
 5. In a furnace as set forth in claim 1, said lower shell portion having a sealing face horizontally extending about said open upper end thereof, and formed with two spacedly juxtaposed annular grooves, said upper shell portion including two annular ribs respectively received in said annular grooves in said adjacent position of said upper shell portion, whereby an annular portion of said sealing face between said grooves is protected by said upper shell portion in said adjacent position of the same, said valve member when in the operative position sealingly engaging said annular portion of said sealing face. 